Conventionally, there has been an antenna apparatus which includes a printed circuit board having a ground plate on which an electric circuit of a communication terminal is mounted, a radio frequency (RF) power source mounted on the printed circuit board, and a variable reactance element mounted on the printed circuit board and located in an opposite area from the RF power source. One end of the RF power source is connected to one end of the ground plate, and one end of the variable reactance element is connected to the other end of the ground plate.
The antenna apparatus further includes a first connector of which one end is connected to the other end of the RF power source, a second connector of which one end is connected to the other end of the variable reactance element, and a dielectric body or a ground body to which the other end of the first connector or the second connector is connected.
The RF power source, the first connector, the ground body, the second connector, the variable reactance element and the ground plate form a current path, and thereby a loop antenna is formed which uses the ground plate as a radiation element.
The conventional antenna apparatus as described above is used in a reader writer which reads a radio frequency identifier (RFID) tag, for example.
Accordingly, it is difficult to install the conventional antenna apparatus in a card type data communication apparatus of which a connector is inserted into the card type data communication apparatus in order to connect the card type data communication apparatus to an information processing apparatus such as a personal computer (PC) or the like.
In order to install an antenna apparatus in the card type data communication apparatus which is connected to the information processing apparatus such as the PC or the like, it is required that the antenna apparatus can be installed in a limited small space of the card type data communication apparatus and can provide high communication performance.
For example, according to a data communication terminal apparatus including a main antenna and a sub-antenna that use a multiple-input multiple-output (MIMO) technique, it is easy to obtain good antenna characteristics by locating the main antenna away from a connector of the data communication terminal apparatus. On the contrary, since the sub-antenna is located away from the main antenna, it is difficult for the sub-antenna to obtain good antenna characteristics.
In general, it is not easy for an antenna which is located close to an information processing apparatus including ground wirings to obtain good antenna characteristics. Accordingly, in the antenna apparatus which uses MIMO technique as described above, the main antenna having priority order is located away from the information apparatus, and the sub-antenna is located close to the information processing apparatus so that a correlation between the main antenna and the sub-antenna is lowered.